The development of an in vitro assay system for nonmutagenic carcinogens is the primary focus of this laboratory. The system involves the use of undifferentiated embryonal carcinoma cells which are known to undergo changes in transcription and gene expression when exposed to certain chemicals. Two of these changes, cell differentiation and provirus transcription/expression, are being studied as assay endpoints. The goal is to determine if the ability of a chemical to cause neoplasia is related to its ability to cause either of the above changes.